The present invention pertains to magnesium halide catalyst supports, catalysts prepared therefrom and a process for polymerizing olefins in the presence of such catalysts.
Magnesium halide catalyst supports have been previously prepared by reacting a halide source with magnesium components represented by the formula R.sub.2 Mg.xAlR.sub.3 wherein x has a value from 0.001 to 10 (U.S. Pat. No. 4,250,288).
It has now been discovered that when .alpha.-olefins are polymerized in the presence of supported transition metal catalysts wherein the support is prepared from the aforementioned magnesium component wherein the atomic ratio of Al:Mg is from about 0.025:1 to about 0.25:1 and wherein said magnesium component is combined with a halide source under conditions such that the reaction temperature does not exceed about 60.degree. C. that the efficiency of the resultant catalyst is much improved.